For the data dumps, maybe rewriting the images needs to be done when generating the HTML, not in the Markdown code itself? (Just like when rendering bare URLs into clickable links with a full title, or when using [tag:tag-name].)

Some users very nicely link cropped images to full versions, or link images to web pages. It would be nice if that is still possible. (So, automatic linking should be smart to detect that.)

Maybe the (bottom) link border can be removed/changed in the CSS?

Maybe large images can be shown in a smaller size right away? Like if the height exceeds some limit, then set it:

Maybe the alt text and optional title can be prompted for as well? Too many images simply have the default "alt text", which is not helping the visually impaired. And sane browsers will not display the alt text in a tooltip, so asking for both alt text and optional title might be nice?

In the alternative syntax, using the very same [x] reference twice, is currently automatically changed into two different [x] and [y] references when adding a new link or image using the toolbar. Hence when really changing the Markdown text source (rather than when generating the HTML, which I'd vote for), then I guess two references need to be inserted when using the alternative syntax: